Diffusion in concentrated lattice gases. V. Particles with repulsive nearest-neighbor interaction on the face-centered-cubic lattice

Abstract

The diffusion of particles in concentrated lattice gases is studied by Monte Carlo methods, assuming a fcc lattice with repulsive nearest-neighbor interaction. Particular attention is paid to the influence of ordering on the diffusion properties, since the model has ordered superstructures at low temperatures $T$ near the stoichiometric concentrations $c=\frac{1}{4}, \frac{1}{2}, \mathrm{and} \frac{3}{4}$. Both the self-diffusion of tagged particles and the collective diffusion by which concentration fluctuations decay are obtained. In the ordered regions both diffusivities are rather small due to a strong decrease of the effective jump rate of the particles. The correlation factor $f(T,c)\mathrm{}$ for self-diffusion has a pronounced non-monotonic concentration dependence for low temperatures. This is interpreted by reducing the problem near $T=0\mathrm{}$ and the limits $c\to \frac{1}{4}-,\frac{1}{2}-$ to an effective single-vacancy problem, and $c\to \frac{1}{4}+,\frac{1}{2}+$ to an effective single-particle problem. Other lattices are briefly discussed.